The present invention relates to scaffolds and particularly to latch mechanisms for attaching scaffold platform trusses to supporting structures which are conventionally two vertical ladders. More particularly, the invention relates to scaffold latch mechanisms that lock in a locking position and include a blocking mechanism to maintain the latch mechanism in the locking position. A typical scaffold is a prefabricated, modular, mobile, rectangular work platform on wheeled, locking casters. A scaffold typically comprises two vertical ladders each having two vertical legs connected by five horizontal rungs, caster stems inserted into bushings located at the bottom of each ladder leg, and two horizontal trusses attached to the vertical ladders to form a rectangular frame. Each horizontal truss is formed to provide an interior ledge on the long axis of the horizontal truss. The platform upon which the user (worker) stands is supported on the truss ledges. The overall dimensions of the rectangular frame can be altered by using different length vertical ladders, horizontal trusses and platforms.
The present invention is a latch mechanism for attaching the horizontal trusses to the vertical ladders.
Scaffolding is used in many applications to provide an elevated support surface for workers. Originally, scaffolding was made from timber, but in recent times metal has become the material of choice for manufacturing scaffolding. Metal scaffolding typically includes a pair of vertical legs and a plurality of horizontal rungs extending between the support legs to form a ladder-like supporting structure. Horizontal platforms extend between, and are attached to, a pair of the ladder-like supporting structures.
Various methods have been used to attach the horizontal platforms or platform trusses to the supporting structures. One widely used method for attaching the platforms to the supporting structures is to provide a framework for the platforms and to form apertures in the platform framework and in the vertical legs of the supporting structure. When the apertures in the platform framework and the vertical legs of the supporting structure are aligned, latch pins can be inserted through the apertures to hold the platform in position relative to the supporting structure. In this description, and in the appended claims, terms such as "frame member" or "horizontal platform framework" are intended broadly to refer to frameworks, trusses or support members for supporing a work platform.
It is known that in the ordinary use of the scaffolding, movement of workers on the platform can cause the supporting structure to move relative to the platform. This relative movement sometimes caused the latch pin to "walk" out of the apertures. Unfortunately, there has been no way to determine whether the latch pin is "walking" out of the apertures except by close visual scrutiny. When the latch pin walked far enough, the platform framework was no longer attached to the supporting structure.
One method for solving the walking problem is disclosed in U.S. Pat. No. 3,396,817 issued to Perry on Aug. 13, 1968. Perry solved the walking problem by rigidly attaching a threaded disk to the latch pin and rigidly attaching a threaded nipple to the platform framework. The threaded disk engages the threaded nipple to hold the latch pin in position in the apertures. However, human nature being what it is, workers oftentimes ignored the threading mechanism, and the latch pins were still allowed to walk out of the apertures.
A latch mechanism was needed that could positively hold a latch pin in position without the use of a threaded disk and nipple. One such latch pin is disclosed in U.S. Pat. No. 4,793,438 issued to Perry on Dec. 27, 1988. The Perry '438 patent discloses a latch pin that is biased by a spring to extend through the aligned apertures in the platform framework and the supporting structure. A release lever engages the latch pin to move the latch pin against the biasing force of the spring in order to disengage the latch pin from the supporting structure.
Unfortunately, this mechanism does not provide a positive indication that the latch pin is properly positioned. Moreover, due to the number of parts, the mechanism was expensive to manufacture. A less expensive and more easily manufacturable latch mechanism is desirable. Furthermore, a latch mechanism that provides a positive indication of the latch pin position and combines the threaded disk and nipple with an automatic blocking mechanism for maintaining the latch pin in a locking position would be a substantial improvement over conventional scaffolding latch mechanisms.
According to the present invention, a latch mechanism for use in coupling a horizontal platform to a vertically extending supporting structure comprises a frame member and means for locking the frame member to the supporting structure. The locking means is coupled to the frame member and is movable between a locking position and an unlocking position. The mechanism also includes means for selectively blocking the locking means in the locking position. The blocking means is coupled to the frame member and includes aperture means for receiving the locking means and means for coupling the blocking means to the frame member. The blocking means is movable between a releasing position for allowing the locking means to move to the unlocking position and a blocking position for retaining the locking means in the locking position.
The frame member includes an engaging member for engaging the supporting structure and a plurality of walls arranged to define an enclosed area. First and second walls of the plurality of walls are positioned in parallel spaced-apart relation perpendicular to the longitudinal axis of the engaging member and include apertures for receiving the locking means. The locking means includes a latch pin positioned inside the enclosed area and positioned between the first and second walls to extend through the apertures in the first and second walls.
The coupling means includes a housing member coupled to the first wall and positioned outside the enclosed area and means for attaching the housing member to the first wall. The housing member defines a channel and includes an aperture coaxially aligned with the apertures in the first and second walls for receiving the latch pin when the latch pin is in the unlocking position. When attached to the first wall, the housing member and the first wall cooperate to form a cavity therebetween.
According to one aspect of the invention, the locking means includes an internally threaded disk rigidly attached to the latch pin and an externally threaded nipple rigidly attached to the second wall. The threaded disk engages the threaded nipple to hold the latch pin in the locking position.
According to another aspect of the invention, the blocking means includes means for visually indicating the position of the latch pin when the latch pin is in the locking position. The indicating means includes a plate positioned in the cavity and sized and oriented for movement by gravity actuation from a latch pin-releasing position to a latch pin-blocking position. The plate includes a solid portion, an elongated aperture and a distal end. The means for coupling the housing member to the first wall includes means for limiting the amount of movement of the plate wherein the limiting means extends from the housing member through the elongated aperture to the first wall.
The elongated aperture can be aligned with the apertures in the housing member and the first and second walls to permit movement of the latch pin between the locking position and the unlocking position. When the solid portion is aligned with the apertures in the housing member and the first and second walls, the latch pin is prevented from moving out of the locking position. At the same time, the distal end extends beyond the cavity to provide a visual indication that the latch pin is in the locking position.
By providing a plate member having a solid portion and an elongated aperture, the present invention selectively blocks the latch pin from walking out of the locking position. By providing a distal end of the plate for extending beyond the cavity when the latch pin is in the locking position, the present invention also provides a positive visual indication of the position of the latch pin.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.